A turbomachine, in mechanical engineering, is a machine that transfers energy between a rotor and a fluid, including both turbines and compressors. While a turbine transfers energy from a fluid to a rotor, a compressor transfers energy from a rotor to a fluid. The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and impart rotational energy to the rotor. Thus, the blades are responsible for extracting energy from—in particular in gas and steam turbines—the high temperature, high pressure gas flowing through the turbine.
Turbine blades are subjected to very strenuous environments, particularly inside a gas turbine. They face high temperatures, high stresses, and a potentially high vibration environment. All three of these factors can lead to blade failures, which can destroy the engine, and turbine blades are carefully designed to resist those conditions. Therefore, the turbine blades are often the limiting component of gas turbines. To survive in this difficult environment, turbine blades often use exotic materials like superalloys and many different methods of cooling, such as internal air channels, boundary layer cooling, and thermal barrier coatings.
In addition, regarding turbine blade vibration, a continuous monitoring of the blade vibration during operation of turbine is usually done to detect resonant and potentially damaging vibrations early and to be able to counteract. To avoid interference with the operation of the turbine, this is usually done by means of Blade Vibration Tip Timing Measurement (BVTTM) systems that are used for contactless measurement of blade vibration amplitudes and to determine blade assembly vibration frequencies. These systems can be applied to both steam turbines and gas turbines, the application however not being limited to those types of turbomachines.
A BVTTM system in principle usually measures the run time of the tip of the rotating blades between at least two circumferential sensors to a very high precision. Vibrations of the blades will result in shorter or longer run times. These run time variations are measured and used to calculate blade vibration amplitudes. BVTTM systems usually include at least four main components:                Multiple sensors (including power supply, cooling, cabling, signal converters, etc.),        Trigger logic and time-of-arrival measurement hardware or software algorithms,        Real time data analysis and data display device including data storage, and        Off-line data analysis software.        
The complete measurement chain from the sensor to the displayed and stored results is subject to numerous error sources, which can have substantial impact to the final result. Special attention has to be paid to the mathematical algorithms which are implemented in the software. These mathematical routines are highly complicated and make use of indirect and iterative computation algorithms which are often random based and use empirical assumptions and hypothesis. Consequently, the behaviour of the system is not fully predictable and the measurement accuracy is unknown under special circumstances and sensor probe setups. In the extreme, this can result in a complete failure of the displayed results, either in amplitude or in frequency.
Therefore, BVTTM systems often fail to produce correct results starting from the first day of operation of a new turbomachine and have to be calibrated and adjusted to the particular turbomachine they are installed in during the first run. This of course is a security risk because vibrations may not be properly detected and damage to the turbomachine may occur during the first run, in particular when e.g. a new turbine prototype with unknown mechanical properties is tested.
In principle, this problem could be solved by calibrating the BVTTM system prior to operation by feeding artificially created and thus known input signals to the BVTTM system, checking the results produced by the BVTTM system and fine-tune the system while comparing its results to the known input. In general, pulse generators using digital or analogue techniques or a combination of both could be used for creating these input signals.
However, it turns out that methods for generating a pulse signal sequence available in the prior art are unable to produce the pulse signals required for calibration of a BVTTM system. The reason for this is the specific nature of the raw signals detected by the sensors. The pulse sequences need to be created with a time precision in the nanosecond range, which requires pulse generators with a processor unit with clock frequencies in the triple-digit megahertz range, i.e. more than 100 million processor cycles per second. In addition, the time differences between the pulses are non-periodic when arbitrary vibration frequencies are simulated. As BVTTM systems require several seconds of measurement time for proper function, this means that several thousand to hundred thousand pulses with different time intervals have to be created. Due to the fact that BVTTM systems require at least two sensors, these pulse signal sequences have to be created for a plurality of channels simultaneously.
The problem needed to be solved is to provide a method for generating a pulse signal sequence using a processor unit that allows calibrating a tip timing measurement system in a turbomachine in order to increase operational security and lifespan of the turbomachine.